1. [Technical Field]
The present invention relates to a method of discriminating optical discs and an optical disc apparatus in which the kind of an optical disc is discriminated.
2. [Related Art]
Recently, a CD (Compact Disc) comes into widespread use as an optical disc. Discs of the CD system such as a music CD are used in various fields. Usually, a music CD is a playback-only medium. However, also a recordable disc which is called a CD-R is sometimes used as a music CD.
On the other hand, a DVD (Digital Versatile Disc) is known as an optical disc which is suitable for a multimedia application. A DVD is used in a wide variety of fields such as video data, audio data, and computer data. Although a DVD is a disc of the same size (diameter of 12 cm) as a CD, its storage capacity is increased by reduction of the pitch of recording tracks, a data compression technique, and the like.
At present, an optical disc apparatus which is compatible with both a CD and a DVD is being developed. Because of difference in the layer structure of a disc, a CD and a DVD are different from each other in reflectance. Depending on the kind of a disc, therefore, the level of an RF signal which is obtained by an optical pickup is changed, and also optimum values of parameters of various servo systems such as a focus servo system and a tracking servo system are changed.
Therefore, an optical disc apparatus which is compatible with plural kinds of optical discs must be configured so as to, when an optical disc is loaded, correctly discriminate the kind of the optical disc.
In a configuration where an optical disc is housed in a cartridge, discrimination can be easily made by, for example, forming an identification hole in the cartridge. In a configuration where optical discs are not housed in a cartridge and have the same size as in the case of a CD and a DVD, however, such a mechanical detection system cannot be employed. When special parts or mechanisms for discrimination, such as a sensor are disposed, the configuration is complicated and the production cost is increased. Therefore, such a countermeasure is not preferable.
The Unexamined Japanese Patent Application Publication Nos. Hei10-198985 and Hei10-199122 disclose an optical disc apparatus which discriminates between a CD and a DVD on the basis of the time difference between the time when focusing is obtained on the disc surface during a focus search, and that when focusing is obtained on the signal plane. The apparatus disclosed in the publications uses the configuration in which the distance between the surface of a CD and the signal plane is about 1.2 mm and that between the surface of a DVD and the signal plane is about 0.6 mm.
The Unexamined Japanese Patent Application Publication No. Hei9-44982 discloses a disc discriminating method in which a focus search is conducted and the kind of a disc is discriminated by measuring at least two time intervals in a reflected light amount signal.
In the techniques disclosed in the Unexamined Japanese Patent Application Publication Nos. Hei10-198985, Hei10-199122, and Hei9-44982, a track-on state must be set in order to conduct a focus search. In the case where discrimination is to be performed by means of a servo control in a DVD mode, when a CD is loaded, a servo control cannot be performed and discrimination sometimes fails.